Amino resin dispersions

ABSTRACT

A carrier web coated with amino resin wherein at least one surface is resinated is produced by applying a spreadable amino resin dispersion containing 70-90% by weight of amino resin and 30-10% by weight of a liquid dispersant to at least one surface of an uncoated carrier web in an apparatus comprising: 
     (a) unwinding station for unwinding uncoated carrier webs from rotatable supply rolls, 
     (b) means for conveying the uncoated webs comprising a plurality of cooperating pressure rolls rotatably mounted in parallel relationship, 
     (c) a coating means for applying a brushable amino resin dispersion to the web, and 
     (d) a belt press for compression-molding and curing the coated web.

This is a continuation of application Ser. No. 473,969 filed Mar. 10,1983.

The present invention relates to carrier webs, in particular those madeof web-like materials, such as, for example, paper or woven or knittedfabrics, which have been coated with spreadable amino resin disperions.

The invention also relates to the processing of carrier materials thuscoated into surface-finished materials, in particular wooden materials,or into laminated plastics, and thus relates to novel, particularlyeconomical process for preparing such materials with a protective and/ordecorative surface finish.

It is known to use heat-curable amino resins for preparing woodenmaterials with protective and/or decorative surfaces and for preparinglaminated plastics. Materials of this type are used for many and variedpurposes in industry, in particular in furniture manufactured andinternal building work, and have thus attained very considerableimportance.

In surface-finishing wooden materials, a decorative and/or protectivelayer is applied to wood fibre or wood chipboards by impregnatingdecorative paper or fabric webs with aqueous solutions of suitable aminoresins, preferably melamine resins, drying them to a certain volatilecontent, and laminating them onto the boards of the wooden material bymeans of a thermal hardening step during which the compression-mouldingpressure can be about 10 to 100 bar (1 bar=10⁵ Pa=1 kg/cm²) and thetemperature about 120° to 180° C. The aminoplast hardens during thecompression-moulding step, and bonds the paper or fabric web to theboard of the wooden material.

Laminates having a decorative and/or protective surface can be preparedin a similar manner, by pressing by means of thermal hardening thedecorative web, after it has been impregnated with amino resin and thendried, onto several layers of kraft paper which has been impregnatedwith phenolic resin. In this method the compression-moulding pressuresare within a range from about 50 to 150 bar, and thecompression-moulding temperatures are usually about 120° to 180° C. Toincrease the scratch and abrasion resistance, the decorative web iscovered before the compression-moulding step with transparent overlaypaper which has been impregnated with amino resin. In some cases, use isalso made of a layer of barrier paper between decorative web and coreand a layer of backing paper on the reverse face. Melamine/formaldehyderesins are preferably used for impregnating the overlay web and thedecorative web. Overlay and barrier papers can also be used insurface-finishing wooden materials.

The subsequent compression-moulding is carried out by various generallycustomary methods. Thus, for example, multi-daylight presses are used,pressing taking place at 120° to 160° C. in the course of about 5 to 10minutes and temperatures being lowered to 70° to 100° C. before theboards are removed. By using this method, it is already possible toprepare surfaces having a very high degree of sheen, even if knownresins are used. A disadvantage is the long time taken for heating upand cooling down, which leads to long press cycles and increases thecosts of the method. In the so-called short-time method only onedaylight space is compressed at any one time. In this method pressingtakes place at 120° to 160° C. within only 30 to 120 seconds, and theproduct is extracted without the press having been cooled down. Althoughthis press cycle is short and relatively inexpensive, it has so far beenimpossible using known resins to produce the same high surface sheen asin the multi-daylight process with cooling down.

A new production method is the continuous manufacture of so-calledcontinuous melamine laminates on twin-belt presses. In this method, thedecorative web is held between two steel belts and pressed underpressure (10 to 30 bar) and heat (130° to 170° C.) onto a suitablecarrier material, such as, for example, vulcanised fibre, or so-calledfurniture parchments.

The processing of aminoplasts by hot-pressing transforms soluble andfusible aminoplast precondensates into infusible and insoluble products.A crosslinking reaction takes place during this hardening process.However, the rate of this crosslinking reaction is as a rule too low foruse in industry, even at the elevated processing temperature used there,and must therefore be raised by adding hardening agents. In particularthe shortcycle process can only be carried out in the presence ofamounts of about 0.05 to 1% of effective hardening agents. Compoundswhich have an acidic reaction and/or split off an acid are used ashardening agents. Examples of such hardening agents are ammonium saltsand amine salts, such as ammonium chloride, ammonium thiocyanate orethanolamine hydrochloride, and strong organic acids, such asp-toluenesulphonic acid. The use of free acids or of salts which have astrongly acidic reaction results in relatively short pot lives for theamino resin, which is thereby made more difficult to process.

The amino resins used for impregnating the carrier webs, which arefrequently also referred to as aminoplast precondensates, are resinousproducts, or solutions thereof, which are formed by condensing amino- orimino-containing compounds with carbonyl compounds and, if desired, witha lower alkanol. (Compare Kunststoff-Handbuch [Plastics ReferenceManual] volume X, Duroplaste [Thermosetting resins], published by C.Hanser Verlag Munich (1968); and Houben-Weyl, Methoden der organischenChemie [Methods of organic chemistry] volume XIV/2, pages 357 et seq.,published by G. Thieme Verlag Stuttgart (1963)).

Examples of known aminoplast-formers are melamine, urea, thiourea,dicyanodiamide, acetoguanamine, and benzoguanamine. Carbonyl compoundswhich are known to be suitable for the reaction with aminoplast-formersare aliphatic or aromatic aldehydes and ketones, such as, for example,formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde,isobutylaldehyde, benzaldehyde, acetone, and methyl ethyl ketone.Mixtures of various aminoplast-formers and various carbonyl compoundscan also be used for preparing aminoplasts.

Urea and melamine are particularly advantageous and therefore frequentlyused aminoplast-formers; formaldehyde is the preferred carbonylcompound.

Lower alkanols which may be present during the reaction ofaminoplast-formers with carbonyl compounds are those which have 1 to 6 Catoms; lower representatives of this group, namely ethanol and, inparticular, methanol, are favoured for preparing so-called impregnatingresins for the surface-finishing of, for example, wooden materials orlaminated plastics.

The reaction between aminoplast-formers, carbonyl compounds and, ifdesired, an alkanol as a rule takes place in a predominantly aqueousmedium within a weakly alkaline range, and is only allowed to proceed toa stage where the products are still soluble and fusible. As soon asthis state has been reached the condensation is discontinued, forexample by cooling down and bringing the reaction mixture to a weaklyalkaline pH value. The aminoplasts thus prepared, which are not fullycondensed and are therefore also referred to as aminoplastprecondensates, are used in the form of their aqueous solutions, inparticular as impregnating resins, in the laminated plastics industryand for surface-finishing wooden materials.

The most important characterising features of amino resins are the molarratio of aminoplast-former to, for example, formaldehyde and the degreeof condensation, which is signified by the water-dilutability of theresin. Modern commercially available resins used for the purposesdescribed above normally have aminoplast/formaldehyde molar ratios of1:1.5 to 1:2.2 and water-dilutability of 1:0.5 to 1:2.0.

industrially used amino resins, in addition to the aminoplastprecondensate, frequently also contain so-called modifiers, which impartspecial propeties to the resins or to the materials prepared from theresins. For instance, the resins can contain additives which lengthenthe pot life, which starts when the hardening agent is added, such as,for example, certain amines, or additives which increase sheen andresilience or further improve weather resistance. Other known additivesaffect the wetting properties of the resins or their flow and hardeningcharacteristics.

Examples of known modifiers are the lower alkanols already mentioned,glycols, glycol ethers, sorbitol, sugar, caprolactam,methylenebisformamide, amidosulphonic acid, p-toluenesulphamide, and thelike.

Amino resins are marketed either in the form of aqueous solutions havinga solids content of about 50-60% by weight, namely as so-called "liquidresins", or, after spray-drying, as anhydrous pulverulent resins, namelyso-called "powder resins".

Pulverulent resins have been preferred in particular when the resinshave to be transported over long distances to where they are to be usedor when a particularly long shelf life is required.

The impregnation of the carrier webs, which is necessary in all knownmethods of processing amino resins, was hitherto effected exclusively bymeans of the so-called "dipping" in special, very expensive impregnatingunits. If pulverulent resins were used they first had to be dissolved inwater. Only the clear, relatively low-viscosity solutions thus obtainedwere then used in the impregnation.

In conventional impregnating, the carrier webs, in addition to theresin, contain so much water that immediate further processing isimpossible. For this reason, the impregnated webs always have to bedried between the impregnating step and the pressing step. They are as arule dried in moving-product dryers which are connected in series, whichdrying is a very energy-consuming process because of the amount of waterto be removed by drying and water's high heat of evaporation. Inaddition, the drying time required necessitates a relatively expensivedrying unit and/or restriction of the production speed.

The amount of energy consumed in drying impregnated carrier websconstitutes a very substantial load on the overall production processespecially when powder resins have to be used, since in this case theheat of evaporation has to be overcome twice: once in spray-drying theresin and once in drying the impregnated carrier web. However, even ifproduction is carried out on the basis of liquid resins, that is ofaqueous resin solutions as obtained in the preparation of the resin oronly moderately concentrated resins, drying the impregnated carrier webis an awkward step, and can, in certain circumstances, be responsiblefor slowing down production. The overall economics of this drying stepare also unfavourable, since drying the resins by means of spraying atthe resin manufacturer's will as a rule consume less energy than dryingthe resinated carrier web at the processor's, not only for reasons ofmachine design but also for kinetic and thermodynamic reasons.

It has now been found that in processing amino resins into coatedmaterials and laminates it is surprisingly possible to avoid theexpensive impregnating of carrier webs and the energyand time-consumingdrying of the impregnated carrier webs when the carrier webs are coatedwith spreadable amino resin dispersions

According to the invention, a particularly favourable way of preparingcarrier webs which are resinated at the surface is to apply to thesurface of the carrier a spreadable dispersion of a pulverulent aminoresin and the liquid phase of which also contains or can also containaminoplast precondensate which acts as an adhesion promoter.

The amount of resin dispersion applied to the carrier web depends,within certain limits, on the weight per unit area of the uncoatedcarrier material, namely on the so-called raw weight. As a rule thecarrier webs are coated with an amount of dispersion which is equal to50 to 150% by weight of the raw weight, preferably 70 to 140% by weightof the raw weight. Accordingly, the amount of dispersion applied to acarrier web with a weight per unit area of 100 g per m² is, for example,50 to 150 g, preferably 70 to 140 g, per m².

The webs thus obtained can be further processed directly, that iswithout intermediate drying, in a conventional manner by hot-pressing.

The present invention also relates to a process for preparing coatedmaterials, in particular wooden materials and laminated plastics, byusing web- or fabric-like carrier webs resinated according to theinvention and subsequently pressing them onto the material to be coated,in particular wooden material, or jointly compression-moulding severalresinated carrier webs, in particular decorative and core webs, intolaminated plastics under the influence of heat.

In addition to immediately further processing the carrier webs accordingto the invention, which have been coated on the surface with spreadableamino resin dispersions, it is also possible to lay in stocks of thesecarrier webs, which are further processed as required, at various placesand at various times. This method of working requires the interpositionof separating (release) films.

The webs resinated at the surface with spreadable amino resindispersions only contain a very small amount of moisture, in particularwater, so that even short drying in the air without the supply ofadditional heat leads to non-tacky surfaces and products which can bestored. It is of course also possible to supply energy and thusaccelerate the evaporation of the small amount of water present.However, the energy consumed is in this case minimal. However, it iswithout doubt particularly economical to combine the surface resinationof the carrier web with the immediately subsequent further processingthrough conventional compression-moulding, since it is in this waypossible completely to dispennse with an intermediate drying step.

The carrier webs coated at the surface with amino resin are prepared byapplying spreadable amino resin dispersions to the surface of thecarrier web. In principle the resin can be applied to both sides of thecarrier web; but it is advantageous, and without any disadvantage asregards further processing, to apply the resin only to one side of thecarrier web, preferably the upper side. The resin dispersion can inprinciple be applied in any manner which is known for the uniformapplication of spreadable dispersions to sheet-like structures. Forinstance, the resin dispersion can be manually brushed on or spread on,preferably by means of a serrated spatula. The application by machine,of advantage in production processes, can be effected, for example, bymeans of a roll with metering by doctor blade.

The spreadable amino resin dispersions used according to the inventionconsist to 70 to 90% by weight of amino resin and to 30 to 10% by weightof a liquid phase, preferably water.

The spreadable dispersions preferably consist of 75 to 85% by weight ofresin and 25 to 15% by weight of water. Accordingly, to prepare 100parts by weight of these dispersions 70 to 90 parts by weight,preferably 75 to 85 parts by weight, of a pulverulent amino resin can behomogenised with 30 to 10 parts by weight, preferably 25 to 15 parts byweight, of the liquid phase, preferably water. If a liquid amino resinsolution (so-called liquid resin) is used as the liquid phase, theamounts of powder resin and liquid resin to be homogenised arecalculated in such a way according to the resin content of the liquidresin that the abovementioned composition of the resin dispersion to beused according to the invention is obtained. Thus, for example,spreadable amino resin dispersions according to the invention can beprepared by homogenising per 100 parts by weight of dispersion 35 to 65parts by weight, preferably 50 to 42 parts by weight, of amino resinpowder with 65 to 35 parts by weight, preferably 50 to 58 parts byweight, of an aqueous aminoplast liquid resin having a resin content of50 to 65% by weight. The amino resin content is then obtained by summingthe amount of powder resin and the resin content contained in the liquidresin.

Preferred spreadable amino resin dispersions are those which contain theresin powder in a state of dispersion in an amino resin solution (liquidresin). They are highly viscous to pasty homogenised amino resindispersions. The liquid phase for the dispersions can be not only wateror aqueous amino resin solution but also other liquids which completelyor incipiently dissolve the powder resin, such as, for example, mixturesof water with low-boiling water-soluble organic solvents.

What the most desirable physical macroscopic state is for the dispersiondepends to a certain extent on the method of application. If thedispersions are brushed on or spread on they can be pasty and contain avery small amount of liquid, while machine application by rolls and, ifdesired, doctor blades favours viscoelastic dispersions which containsomewhat more liquid. The dispersions preferably have an apparentviscosity of 10,000 to 14,000 mpa.s within the shear range from 16.5 to1.5 sec⁻¹.

A suitable powder resin for preparing amino resin dispersions accordingto the invention is almost any plastified, pulverulent aminoplastprecondensate which has not yet been fully hardened, that is which isstill fusible, and thus virtually a majority of the commerciallyavailable amino resin types which are suitable for preparing coatedmaterials and laminated plastics using the conventional process.Similarly, commercially available impregnating resins can be used asliquid resins in the preparation of the resin dispersions according tothe invention.

Such commercially available powder and liquid resins have as a rule amolar ratio of aminoplast-former to formaldehyde of 1:1.5 to 1:2.2,preferably 1:1.6 to 1:1.8, and water-dilutability within the range from1:0.8 to 1:1.5.

The amino resins used for preparing spreadable resin dispersions to beused according to the invention are predominantly based on melamine orurea as the aminoplast-former. Even mixed resins which contain melamineand urea as aminoplast-formers are suitable. Resins based on puremelamine/formaldehyde precondensates which can, if deisred, also containknown modifiers are particularly useful and higherly suitable forpreparing high-quality end products.

Powder resins can be homogenised with the liquid phase desired in aconventional manner, for example in stirred or kneading units.

Any customery web-like or woven or knitted sheet-like structures aresuitable for use as a carrier material in the preparation ofsurface-resinated carrier webs according to the invention. Inparticular, virtually any conventional plain and printed decorativepaper having a raw weight of 40 to 200 g/m², and, to a limited extent,overlay paper (20-40 g/m²) can be processed.

Those paper grades are also highly suitable which, while in the pulpstate during their manufacture, have already been finished so as to besubstantially non-splitting.

The carrier webs according to the invention, which are coated with aspreadable amino resin dispersion, can be processed merely by usingknown and conventional methods, either immediately, without intermediatedrying, or after storage. Thus, for example, a pack of 2 to 6 carrierwebs is continually compression-moulded under the influence of pressureand heat on twin-belt presses into laminated plastics intended fordecorative or industrial use.

The carrier webs can also be processed in multi-daylight and, inparticular, so-called short-cycle presses, for example in the form of adesign which comprises 1 to 3 layers (decorative and underlay films) andwhich is intended for surface-coating wooden materials. In the course ofthe coating step the flow of the resin in the amino resin dispersionforms a protective surface and brings about optimal adhesion to the corematerial or carrier board.

It was very surprising that resin flow during the short transitionperiod from still fusible aminoplast precondensate to infusible,thermoset resin is sufficient to produce a completely homogeneous,non-splitting laminated product.

A further unexpected benefit of using carrier materials according to theinvention, which are surface-coated with spreadable amino resins, isthat the laminated products obtained, in particular laminated plasticsproduced therefrom, are highly flexible, a feature unknown in the caseof thermoset laminates. The novel spreadable amino resin dispersionsthemselves can also be applied as a top coat to decorative papers whichhave been pre-impregnated by known methods, for example with melamineresin, and then dried and which have raw weights of 50-150 g/m² or topre-impregnated cardboard having raw weights of 150-350 g/m².

The examples which follow illustrate the present invention. They can ofcourse also be varied within the definition of the above disclosure andin accordance with general know-how.

EXAMPLE 1

80 parts of a modified commercially available melamine/formaldehydeshort-cycle resin in powder form (molar ratio of melamine toformaldehyde=1:1.8) and 20 parts of demineralised water were dispersedby means of a high-speed stirrer to give a clot-free resin dispersion.Viscosity at 23° C.: about 12,000 to 14,000 mpa.s. 0.7% of themorpholine salt of para-toluenesulphonic acid, as a hardening agent, and0.5% of a commercially available wetting agent were added to thisdispersion.

The pot life of the dispersion at 20° to 25° C. was about 8 to 10 hours.The batch described above was applied by means of a roll with doctorblade metering (100 to 150 μ) to the upper face of the followingcommercially available types of decorative paper:

(a) Sapeli woodgrain-printed decorative paper

Raw weight: 65 g/m²

Final weight, including dispersion: 140 g/m²

(b) White decorative paper

Raw weight: 80 g/m²

Final weight, including dispersion: 170 g/m²

(c) Grey decorative paper printed with a linen pattern

Raw weight: 120 g/m²

Final weight, including dispersion: 250 g/m²

(d) Cotton fabric

Raw weight: 200 g/m²

Final weight, including dispersion: 440 g/m²

(e) Core paper already finished in the course of its manufacture so asto be non-splitting

Raw weight: 190 g/m²

Final weight, including the coat of resin dispersion: 350 g/m²

(f) Regenerated paper

Raw weight: 140 g/m² (used as an underlay film)

Final weight, including the coat of resin dispersion: 290 g/m²

(b) The individual layers of paper were immediately compression-mouldedonce the dispersion had been applied, that is they were not dried inbetween.

(b 1) Sequence of layers for preparing a laminate:

Platen (silk gloss) or aluminium foil or textured paper

Decorative paper or fabric (grade a-d) with the resinated side facingupwards

Regenerated paper (grade f)

Core paper (grade e)

Platen

Compression-moulding conditions: 25 to 35 seconds at 155°-150° C.,measured at the decorative paper under a moulding pressure of 25-30 bar.

Result:

Laminates were obtained which were void-free and non-splitting and had ahomogeneous continuous surface.

The degree of hardening was examined by means of the Kiton dyeing test,the result, which was at level 2, being within the usual range. Thestream resistance test and the crack resistance test, which were bothcarried out in accordance with prescribed methods, namely DIN 53,799 andDIN 68,765 respectively, satisfied in the requirements.

(b 2) Sequence of layers for preparing a laminate using vulcanised fibreor furniture parchment as core layer:

Structural paper or aluminium foil

Decorative paper or fabric (grade a-d) with the resinated side facingthe structural paper

Vulcanised fibre or furniture parchment

Regenerated paper (grade f)--resinated side facing the vulcanised fibrelayer

Processing conditions in a twin-belt press:

Residence time under pressure and heat: about 20 seconds, whichcorresponds to a linear speed of 6 m/min. The temperature at the twomoulding belts was 160°-165° C.

Result:

Laminates were obtained which were void-free and non-splitting and had ahomogeneous continuous surface.

The degree of hardening was examined by means of the Kiton dyeing test,the result, which was at level 2, being within the usual range.

The steam resistance test and the crack resistance test, which were bothcarried out in accordance with prescribed methods, namely DIN 53,799,satisfied the requirements.

It is noteworthy that not only the laminates prepared in accordance withthe invention according to Item (b 1) of Example 1 but also thelaminates prepared in accordance with the invention according to Item (b2) of Example 1 are distinguished by a high degree of flexibility, forwhich thermoset laminates are normally not known.

(b 3) Sequence of layers for coating chipboard

Release paper (textured film)

Decorative papers (a-c), resinated side facing textured film

Regenerated paper (f), resinated side facing chipboard

Chipboard

Decorative papers (a-c), resinated side facing textured film

Release paper (textured film)

Moulding conditions: 48 seconds at 160° C., measured at the decorativepaper

Moulding pressure: 25 bar

Result:

Coated chipboard was obtained which had a homogeneous continuous surfacewith firm adhesion to the chipboard. The degree of hardening wasexamined by means of the Kiton dyeing test, the result, which was atlevel 2, being within the usual range. The steam resistance test andcrack resistance test, which were both carried out in accordance withprescribed methods, namely DIN 53,799 and DIN 68,765 respectively,satisfied the requirements.

Comparison:

Laminates were prepared using the layer sequences specified, except thatthe individual papers were treated in a known prior art manner wherebythey were thoroughly impregnated with a 55% strength aqueous melamineimpregnating resin solution containing added hardening agent and wettingagent and then dried to a volatile content of 6.5% (dried at 160° C. for5 minutes).

The compression-moulding likewise took place under the abovementionedconditions.

Result:

There were no observable differences in application properties (Kitontest, steam test, crack resistance test) between the laminates preparedaccording to the invention from carrier webs treated with a brushableresin dispersion and the laminates prepared by conventional methodsusing thoroughly impregnated and dried carrier webs.

Example 2

85 parts of a modified melamine/formaldehyde resin containing 15% ofurea (molar ratio of aminoplast former to melamine=1:1.8) in powder formand 15 parts by weight of demineralised water were dispersed by means ofa high-speed stirrer to give a clot-free resin dispersion. Viscosity at23° C.: about 12,000-14,000 cp. 0.7% of the morpholine salt ofpara-toluenesulphonic acid, as a hardening agent, and 0.5% of acommercially available wetting agent were added to this dispersion.

The pot life of the dispersion was at 20°-25° C. about 8-10 hours. Thebatch described above was applied by means of a roll with doctor blademetering (100 or 150μ) to the upper face of the following commerciallyavailable types of decorative paper:

(e) Core paper already finished in the course of its manufacture so asto be non-splitting

Raw weight: 190 g/m²

Final weight, including the coat of resin dispersion: 350 g/m²

(f) Regenerated paper

Raw weight: 140 g/m² (used as an underlay film)

Final weight, including the coat of resin dispersion: 290 g/m²

The resinated papers were compression-moulded without intermediatedrying together with an undried decorative paper (grade a-c) resinatedas in Example 1 using the following sequence of layers:

Platen (silk gloss) or aluminum foil or textured paper

Decorative paper or fabric (grade a-d), resinated face upwards

Regenerated paper (grade f)

Core paper (grade e)

Platen

Compression-moulding conditions: 25 to 35 seconds at 155°-250° C.,measured at the decorative paper under a moulding pressure of 25-30 bar.

Result:

Laminates were obtained which were void-free and non-splitting and had ahomogeneous continuous surface. The degree of hardening was examined bymeans of the Kiton dyeing test, the result, which was at level 2, beingwithin the usual range. The steam resistance test and the crackresistance test, which were both carried out in accordance withprescribed methods, namely DIN 53,799 and DIN 68,765 respectively,satisfied the requirements.

EXAMPLE 3

55 parts by weight of a modified commercially availablemelamine/formaldehyde short-cycle resin (molar ratio of melamine toformaldehyde=1:2.0) in powder form and 45 parts by weight of acommercially available modified melamine/formaldehyde liquid resin(molar ratio of melamine to formaldehyde=1:1.75) in the form of a 57%strength aqueous solution were dispersed by means of a high-speedstirrer to give a clot-free resin dispersion.

0.8% of the morpholine salt of para-toluenesulphonic acid, as ahardening agent, and 0.5% of a commercially available wetting agent wereadded to this dispersion.

The method used to apply the dispersion to the carrier webs and theirfurther processing into laminates or coated chipboards where inaccordance with sections (b1), (b2) and (b3) of Example 1.

The compression-moulded products obtained were free of voids andnon-splitting and had a homogenous continuous surface. The degree ofhardening was examined by means of the Kiton dyeing test, the result,which was at level 2, being within the usual range. The steam resistanceand the crack resistance conformed to the requirements of DIN 53,799 andDIN 68,765 respectively.

EXAMPLE 4

55 parts by weight of a modified commercially availablemelamine/formaldehyde short-cycle resin (molar ratio of melamine toformaldehyde 1:1.8) in powder form and 45 parts by weight of acommercially available modified melamine/formaldehyde liquid resin(molar ratio of melamine to formaldehyde 1:1.7) in the form of a 57%strength aqueous solution were dispersed by means of a high-speedstirrer to give a clot-free resin dispersion.

0.8% of the morpholine salt of para-toluenesulphonic acid, as ahardening agent, and 0.5% of a commercially available wetting agent wereadded to this dispersion.

The dispersion was applied to the surface of a white decorative paper(raw weight: about 80 g/m²) which, in a known process, had beenimpregnated with a commercially available modified melamine impregnatingresin (molar ratio of melamine to formaldehyde 1:1.7) and dried. Weightafter impregnating and drying: about 150 g/m².

Weight after impregnating, drying and application of dispersion: about200 g/m².

The decorative paper thus treated was further processed into laminatesor coated chipboards as in sections (b1), (b2), and (b3) of Example 1.

Result:

The laminates and coated chipboards obtained in this example wereequivalent to the products of Example 1, having void-free homogeneouscontinuous surfaces and degree of hardening level 2. The resistance tosteam, the crack resistance, an the degree of cohesion within thematerial (cohesion between layers) conformed to requirements.

EXAMPLE 5

80 parts of a modified commercially available melamine/formaldehydeshort-cycle resin in powder form (molar ratio of melamine toformaldehyde=1:1.8) and 20 parts of demineralised water were dispersedby means of a high-speed stirrer to give a clot-free resin dispersion.Viscosity at 23° C.: about 12,000-14,000 mpa.s. 0.7% of the morpholinesalt of para-toluenesulphonic acid, as a hardening agent, and 0.5% of acommercially available wetting agent were added to this dispersion.

The pot life of the dispersion at 20°-25° C. was about 8-10 hours. Thebatch described above was applied by means of a roll with doctor blademetering (100 or 150μ) to the upper face of a layer of white foldingcardboard. This cardboard had previously been prime-impregnated in aknown manner using a mixture of equal parts of an acrylate dispersionand a urea impregnating resin and dried.

Raw weight of the cardboard: 210 g/m²

Weight after impregnating and drying: 300 g/m²

Total weight including the surface coat of dispersion: 380 g/m²

The single layer of cardboard was hardened in a twin-belt press underconditions such as those described in part (b2) of Example 1.

Result:

A non-splitting flexible material was obtained which had a continuoushomogeneous surface. The degree of hardening was examined by means ofthe Kiton dyeing test, the result of which was at level 2, being withinthe usual range. Such a product can be processed, inter alia, to coatedge areas.

The use according to the invention of spreadable (relatively lowmoisture content) amino resin dispersions enables the use in industry ofapparatus for preparing laminates or the like which takes up relativelylittle space by virtue of the fact that compression-moulding need not bepreceded by an energy- and time-consuming drying step which makes use ofexpensive drying equipment, such as long drying ducts. A unit to carryout the invention, that is to prepare compression-moulded products usingcarrier webs according to the invention, which are coated with aminoresin, therefore need not have a system for drying the resinated carrierwebs. Such a unit according to the invention thus essentially consistsof only three elements, namely

(a) a unit for removing carrier webs, decorative films and basematerial,

(b) a coating station, and

(c) a press.

All three units can in principle be constructed in a known manner.

The specific embodiment of such a unit described below is intended toillustrate the invention and how it is carried out without, however,restricting the invention to the specific features of this embodiment.

The drawing shows, and describes in more detail, an illustrativeembodiment of apparatus for the continuous production of a carrier webwhich is coated with amino resin in accordance with the presentinvention. In the drawing

FIG. 1 shows a diagrammatic side view of the whole apparatus;

FIG. 2 shows a vertical section through pressure chambers of thecompression-moulding belt device;

FIG. 3 shows a vertical section through a pressure chamber which is inaccordance with FIG. 2, has a shut-off device, and is not under load;

FIG. 4 shows a vertical section through the same pressure chamber as inFIG. 2 under load; and

FIG. 5 shows a vertical section through the same pressure chamber whichhas a modified shut-off device and is not under load.

10 designates an unwinding station for two uncoated carrier webs 11, 12,which comprise an upper supply roll 13 with a reserve roll 14 and alower supply roll 15 with a reserve roll 16. The unwinding carrier webs11, 12, one lying on top of the other, pass through pressure rolls (feedrolls) 17 and 18, which are rotatively mounted parallel and on top ofeach other, and of which preferably one pressure roll is driven, so thattension is exerted on the carrier webs, drawing these carrier webs fromthe corresponding supply rolls.

Downstream of this unwinding station is a coating unit 19 which hastransfer rolls 20 and 21 and which applies to opposite surfaces of thecarrier webs the spreadable amino resin dispersion according to theinvention, which is temporarily stored in storage vessels 23 and 24.

This coating unit is followed at a certain short distance by on the oneside (top side) an unwinding device 25, which has corresponding supplyand reserve rolls 26, 27, from which a textured film 28 according to theinvention is drawn off, and on the other (underside) a similar unwindingdevice 29, which has corresponding supply and reserve rolls 30, 31 F,from which such a film as vulcanised fibre film 28a is drawn off and,like the drawn off structured film 28, is pressed by means of furtherpressure rolls (feed rolls) 34, 35 onto the still liquid amino resindispersion according to the invention.

To compression-mould the carrier webs thus coated under elevated orrelatively high temperatures a compression-moulding apparatus 36(twin-belt press) is located immediately downstream and has twocontinuous circulating compression-moulding belts 37, 38 which areopposite to each other and which are passed round deflection rolls 37a,38a and exert a certain specifically high pressure on the moving carrierwebs 11, 12 G, which have been coated several times, as well as on thetextured film 28 and the base film 28a, compression-moulding these intoa laminate.

To ensure a particularly uniform pressure and to avoid loss of air, alarge number of pressure chambers 46, 47, each with an outer fitting 39and an inner fitting 40, has been fixed on the reverse face of eachcompression-moulding belt 37, 38 to a common pressure plate 41.

The outer fitting 39 and the inner fitting 40 are arrangedconcentrically to each other (compare FIGS. 3 and 4). There is on eachcompression-moulding belt 37, 38 an annular seal 42, which is held bythe inner fitting 40. The seal 42 is located in accordance with FIG. 3of the drawing in a recess of the inner fitting 40. A resilient sealring 43 spans the gap between the inner fitting 40 and the surrounding,outer fitting 39. The inner fitting 40 together with the annular seal 42can thus move without friction by a small amount relative to the outerfitting 39.

According to FIG. 3 of the drawing, an annular space 45, which connectsthe inner pressure chamber 46 to the outer pressure chamber 47, has beenleft free between a support 44, which has a stepped head 44a, and theinner fitting 40. The pressure transfer medium can flow via ducts 48 and49 to the tapholes 50 of the pressure plate 41 and from there through acentral bore 51 of the support 44 and via radial bores 52 of the support44 into the inner pressure chamber 46. From there the pressure transfermedium can pass via the annular space 45 into the outer pressure chamber47, where it presses the compression-moulding belt 37 against theworkpiece.

The pressure in the inner pressure chamber 46 presses the inner fitting40 together with the annular seal 42 against the compression-mouldingbelt 37. The force with which the inner fitting 40 is pressed againstthe compression-moulding belt 37 depends on the pressure and on the areaof the inner fitting 40 which is parallel to the compression-mouldingbelt 37 and within the pressure chamber 46 and on which the pressureacts. This force is opposed by a force which depends on the pressure inthe outer pressure chamber 47 and on the area of the inner fitting 40 onwhich this pressure acts. The pressure in the outer pressure chamber 47causes the compression-moulding belt 37 to be pressed against theworkpiece.

If in the course of operation pressure transfer medium were to escapefrom the outer pressure chamber 47 through a gap between the seal 42 andthe compression-moulding belt 37, this loss of pressure transfer mediumcan be replaced by pressure transfer medium flowing from the innerpressure chamber 46 through the annular space 45 into the outer pressurechamber with a certain pressure-regulating action. The air pressure inthe outer pressure chamber 47 is then somewhat smaller than the pressurein the inner pressure chamber 46. In other words, should an undesirableescape of pressure transfer medium occur in the course of operation fromthe outer pressure chamber 47, then, due to the pressure-regulatingaction of the annular space 45, the pressure difference between theinner pressure chamber 46 and the outer pressure chamber 47 becomeslarger, so that the force which pushes the inner fitting 40 togetherwith the seal 42 perpendicularly onto the compression-moulding belt 37and which is the resultant force of the pressure forces of the innerpressure chamber 46 and the outer pressure chamber 47 becomes larger.

So that in any case the force with which the inner fitting 40 is pushedtowards the compression-moulding belt 37 is greater then the force withwhich this fitting 40 is pushed away from the compression-moulding belt37 a helical spring 53 is mounted in the inner pressure chamber 46 insuch a way that one end acts against the outer fitting 39 and the otherend against the inner fitting 40. In FIG. 3 of the drawing this helicalspring 53 has been given a conical design; it can also be cylindrical.

However, since frequently the pressure-regulating action of the annularspace 45 is inadequate and pressure transfer medium escapes inundesirable fashion, an additional shut-off device in the form of anO-shaped, preferably resilient sealing ring 54 is mounted according tothe invention between the stepped head 44a and the area 40a of the innerfitting 40 which faces the compression-moulding belt, which shut-offdevice seals the annular space 45 when the area 40a, which faces thecompression-moulding belt, approaches the stepped head 44a, so that thepressure exerted by the inner pressure chamber 46 on the inner fitting40 increases (compare FIG. 3).

Such a simple shut-off device enables the feed of pressure transfermedium from the inner pressure chamber 46 into the outer pressurechamber 47 to be controlled in a direct manner by the workpiece,specifically its outer contours, passing through the press.

On entry a workpiece comes into contact, with its edges, with thecompression-moulding belt 37 and lifts the latter onto an area whichcorresponds to the surface of the moving workpiece. This has the effectof raising all inner fittings 40 of the small pressure devices (pressurechambers) located at the edges and on the surface of the movingworkpiece, so that the distance between the area 40a, which faces thecompression-moulding belt, and the stepped, fixed head 44a becomeslarger, and hence the annular space 45 between the inner and the outerpressure chamber 46, 47 opens up (FIG. 4). Accordingly, pressuretransfer medium now flowing into the outer pressure chamber 47 forcesthe compression-moulding belt 37 against the moving workpiece. When theworkpiece has passed through the press the rear edges of the workpiecerelease the inner fitting 40, so that the latter descends and theannular space 45 is re-sealed by the resilient sealing ring 54. Theouter pressure chamber 47 becomes unpressurised and hence does not exerta force on the compression-moulding belt 37, which is not pushed intothe free space (in the absence of a workpiece). The result is that theunfavourable escape of pressure transfer medium is avoided.

In a modified embodiment according to FIG. 5, the support 44, inaddition to the bores 52 for feeding the pressure transfer medium intothe inner pressure chamber 46, has further bores 55, which open andclose according to the height setting of the inner fitting 40, theposition of which is directly controlled by the workpiece passingthrough.

On entry of a workpiece the inner fitting 40 is lifted by the edge ofthe workpiece and unblocks the lower bores 55, so that pressure transfermedium can also flow into the outer pressure chamber 47, where, as inthe illustrative example according to FIG. 4, it forces thecompression-moulding belt 37 against the moving workpiece. Once the rearedge of the workpiece has passed through the inner fitting 40 descendsand hence seals the bores 55. For this purpose, the inner fitting 40 canfit tightly on the support 44. If it is in practice impossible toeliminate a narrow gap between the outer walls of the support 44 and theinner fitting 40, it is advantageous and preferable to insert a sealingring 56 into this gap, in order to avoid unintentional flow of thepressure transfer medium from the inner pressure chamber 46 into theouter pressure chamber 47.

What we claim is:
 1. Spreadable amino resin dispersion containing 70-90%by weight of a solid, modified melamine-formaldehyde resin having amelamine-formaldehyde ratio of from 1:1.5 to 1:2.2 and awater-dilutability within the range from 1:0.8 to 1:1.5 and 30-10% byweight of a liquid dispersant.
 2. Spreadable amino resin dispersionaccording to claim 1 containing 70-90% by weight of a solid, modifiedmelamine-formaldehyde resin having a melamine-formaldehyde ratio of from1:1.5 to 1:2.2 and a water-dilutability within the range from 1:0.8 to1:1.5 and 30-10% by weight of an essentially aqueous dispersant. 3.Spreadable amino resin dispersion containing 35-65% by weight of asolid, modified melamine-formaldehyde resin having amelamine-formaldehyde ratio of from 1:1.5 to 1:2.2 and awater-dilutability within the range from 1:0.8 to 1:1.5 and 65-35% byweight of an aqueous liquid resin, the melamine-formaldehyde ratio offrom 1:1.5 to 1:2.2 and the water-dilutability of 1:0.8 to 1:1.5.
 4. Theprocess for preparing a spreadable amino resin dispersion according toclaim 1 comprising homogenizing 70-90 parts by weight of an amino powderresin with sufficient parts by weight of a liquid dispersant to product100 parts by weight of dispersion.
 5. The process for preparing aspreadable amino resin dispersion according to claim 2 comprisinghomogenizing 70-90 parts by weight of an amino powder resin withsufficient parts by weight of an essentially aqueous liquid to produce100 parts by weight of dispersion.
 6. The process for preparing aspreadable amino resin dispersion according to claim 3 comprisinghomogenizing 35-65 parts by weight of an amino powder resin with 65-35parts by weight of amino liquid resin to product 100 parts by weight ofdispersion.